First, a structure of an electric blower to be used in an electric vacuum cleaner commonly used is described briefly hereinafter with reference to FIG. 5. In FIG. 5, stator 102 is formed of field-magnetic core 103 on which field windings 113 are wound. Armature windings 108 are wound on armature core 107, which is coupled to shaft 106. Armature core 107, armature windings 108 and shaft 106 form rotor 105, which is rotatable because shaft 106 is supported by bearing 110. Shaft 106 is equipped with commutator 109.
Motor-side bracket 112 fixes stator 102, and it also fixes brush holder 114 with screw 115. Brush holder 114 holds a pair of carbon brushes (not shown), which touches commutator 109. Motor 116 is thus formed.
Bracket 112 is equipped with exhaust port 120, and shaft 106 is equipped with centrifugal fan 117, of which outer circumference is provided with air guide 118 forming an air duct. Air guide 118 is formed of diffuser 121, flow changer 122 for guiding airflow to the rear of air guide 118, and return path 123. Diffuser 121 includes a plurality of paths formed of stationary blades 129 of which surfaces are adjacent to each other. Bracket 111 and fan case 119 are prepared on the fan side. Fan case 119 includes intake port 125 for sucking air. Conventional electric blower 101 is thus constructed.
In the construction discussed above, motor 116 is powered from an external source, an armature current runs to armature windings 108 via the carbon brushes (not shown) and commutator 109, and a field current runs through field windings 113 wound on stator 102. The field current prompts field core 103 to produce magnetic flux, and force is generated between the magnetic flux and the armature current running through armature windings 108, so that rotor 105 is rotated.
Rotation of rotor 105 prompts centrifugal fan 117 provided to shaft 106 of rotor 105 to rotate, then the air in centrifugal fan 117 is speeded up and runs through diffuser 121 of air guide 118, where the air is slowed down, then the air enters into flow changer 122, which changes the flow direction of the air by 180°, then the air runs toward motor 116 via return path 123. The air then cools rotor 105, stator 102, and the carbon brushes before the air is exhausted from exhaust port 120 of bracket 112.
The foregoing structure of the conventional electric blower cannot meet the enhancement of efficiency needed for electric blowers to satisfy the higher suction power of the recent home-use vacuum cleaner. Another prior art developed for compensating for the insufficient part of the foregoing structure is disclosed, e.g. in Unexamined Japanese Patent Publication No. 2001-271794. This instance is described hereinafter with reference to FIG. 6, in which similar elements to those in FIG. 5 have the same reference marks and the descriptions thereof are omitted here.
Electric blower 201 shown in FIG. 6 has outwardly falling tabs 136 formed by cutting and raising the upper side of each one of slits 126 outwardly, which slits 126 are provided to the outer circumference of fan case 119, thereby forming openings. Through the openings, the air having passed diffuser 121 is discharged in part to the outside, so that the efficiency of electric blower 201 improves.
However, since the foregoing electric blower has tabs 136 which outwardly falls along the direction from the end of sucking side (upper side of the slit) of slit 126, placed to the outer circumference of fan case 119, to the opposite end (lower side of the slit) to the sucking side, and the openings formed by tabs 136 are opened opposite to a sucking inlet of fan case 119, the openings cannot be large enough to discharge a part of the air having passed diffuser 122 to the outside. As a result, this structure also limits the improvement of the efficiency of the electric blower to a certain degree.